People who grew up in the worst years of the Troubles are the most prone to suicide in Northern Ireland, an international conference on children in conflict has heard.

The legacy of the conflict has resulted in a higher rate of self-harming – particularly in Derry, UK City of Culture in 2013 – among children and young adults who witnessed the violence compared with other British and Irish cities.

Professor Mike Tomlinson, who has studied suicide rates over the last 40 years, told the Children in Conflict conference in Belfast that the overall rate of suicide in Northern Ireland doubled after the IRA's second and decisive ceasefire in 1997.

"There are clear indications from the data … that the levels of psychic distress in Northern Ireland have risen dramatically in the period of the peace.

"This is something of a paradox since we have just learnt that Northern Ireland is the happiest region of the UK," the Queen's University of Belfast academic said.

In his research, Tomlinson said suicide rates for men rose from 13 per 100,000 of the population in 1997 to 24 per 100,000 by 2008.

"Having studied 40 years of data on age, gender and cause of death, my conclusion is that the cohort of children and young adults who grew up in the worst years of violence between 1969 and 1977-78 now have the highest suicide rates and the most rapidly increasing rates of all age groups.

"The highest suicide rate is currently for men aged 35-44, followed closely by the 25-34 and 45-54 age groups," he said.

Tomlinson warned that some of those who witnessed the Troubles as children and teenagers were now turning the violence on themselves during peacetime.

"Those age groups with the highest suicide rates belong to the generations of people who grew up in the conflict and who experienced no other social context until the late 1990s. They are the people who were must acculturated to division and conflict, and to violence," he said.

"In the period of peace, externalised expressions of violence and cultures of authoritarianism have gradually subsided, and to some extent violence has become internalised.

"At present, our young people are responding to the social crisis they face with the labour market not through mass political protest or social disorder, but through private solutions, including emigration, including self-destructive tendencies."

Tomlinson's research compared hospital admissions caused by self-harm in nine cities across Britain, Northern Ireland and the Irish Republic. It found that Derry had the highest such admissions, with 611 in 2009, while Dublin, which is currently suffering an ongoing recession, had 352 admissions in the same year.

Derry's self-harm rate was higher than that of Manchester, Leeds, Oxford, Limerick, Cork, Galway and Waterford.

The conference, which began on Monday at Belfast's Europa Hotel, focuses on the impact on children of violent conflict and social problems in various parts of the world.